Sealing in a hydraulic turbine unit

ABSTRACT

System for providing sealing between a rotor and a turbine casing in a hydraulic turbomachine includes a sealing ring arranged in a peripheral region of the rotor. The sealing ring forms at least one hydrostatic bearing with respect to at least one of the rotor and the turbine casing. The at least one hydrostatic bearing includes at least two bearing surfaces which face one another. At least one of the at least two bearing surfaces is arranged on the sealing ring. At least another of the at least two bearing surfaces is arranged on at least one of the rotor and the turbine casing. At least one groove is formed on at least one of the at least two bearing surfaces. At least one pressure-liquid line is coupled to each of the at least one groove and a pressure-liquid supply. This Abstract is not intended to define the invention disclosed in the specification, nor intended to limit the scope of the invention in any way.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application of InternationalApplication No. PCT/AT01/00293, filed Sep. 14, 2001. Further, thepresent application claims priority under 35 U.S.C. § 119 of AustrianPatent Application Nos. A 1581/2000 filed on Sep. 15, 2000 and A278/2001 filed on Feb. 22, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the sealing-off of the rotor of hydraulicturbomachines, such as turbines, pumpturbines, accumulator pumps orother pumps, with respect to the turbine casing.

2. Discussion of Background Information

Kaplan turbines for low, Francis turbines for medium and Pelton turbinesfor high fall heights form the modem standard repertoire in the field ofturbine construction. Francis turbines in this case cover essentiallythe fall-height range of between 30 m and 400 m.

In this context, Francis turbines reach efficiencies of about 95% in thelower fall-height range and of up to more than 92% in the upperfall-height range. Particularly in the upper fall-height range, the gaplosses and disc friction are responsible for the decrease in efficiencywhich it has hitherto been impossible to eliminate. To explain these twophenomena, the construction and operation of a Francis turbine will bedealt with briefly below:

In Francis turbines, the water driving the turbine flows out of ahorizontally lying spiral through a guide wheel to the rotor. Therapidly rotating rotor converts the pressure and velocity energy of thewater into the rotational movement of the shaft, on which the rotor isfastened, and consequently drives a generator for current generation.The driving water leaves the rotor and also the turbine through asuction pipe downwards in the axial direction.

In the peripheral region of the rotor, at the outer ends of the bladeducts, the latter move at high speed past the stationary turbine casing,and, between these parts, it is not possible to avoid a gap, throughwhich the water coming from the guide blades flows past the rotor andthus passes into the gap-like regions between the outer surface of therotor and the inner surface of the turbine casing. Considerablefrictional losses occur due to the high speed differences between thestationary casing and the rotating rotor. Furthermore, the high pressureprevailing in the upper gap generates a powerful axial thrust whichsubjects the shaft and the axial bearing to extreme load. For thisreason, a labyrinth seal is provided in the outer circumferential regionof the rotor and the water passing through this labyrinth seal is ledpast the turbine. The prior art thus accepts a leakage which, even inmedium-sized turbines, may amount to 0.5 m³/s.

Since, then, for the reason mentioned, the labyrinth seal is arranged inthe outer region of the rotor, the small gap widths which are soughtafter give rise to considerable frictional losses and high brakingtorques. Furthermore, these seals are costly to produce and, preciselyalso because of the high relative speeds between the surfaces locatedopposite one another, are exposed by the impurities repeatedly entrainedand contained in the water, such as sand grains, wood fragments and thelike, to constant wear which makes complicated maintenance work andrepairs necessary.

It is not possible to provide an actual seal in the outer region of therotor in any way other than directly on the shaft which, of course, isled through the casing. The reason for this are, on the one hand, thehigh relative speeds, already mentioned several times, of the componentslocated opposite one another and, on the other hand, the dynamicproblems which arise due to the unavoidable relative movements(transversely to the main rotational movement) in the case of thesedimensions and the forces which occur. These relative movements takeplace essentially in the axial direction and arise in the event ofchanges in the operating state, but also due to tolerances, bearingplay, randomly excited vibrations and the like.

In the electricity generation, then, the question of as high anefficiency as possible is of critical importance, on the one hand,because of commercial considerations and, on the other hand, for reasonsof environmental protection. Of the abovementioned 5 to 7% of the energycurrently not yet utilized and contained in the driving water, acomparatively large fraction, particularly in the case of Francisturbines operating in the range of high fall heights and consequentlypressures, is due to the gap losses and here, in particular, again dueto the losses in the upper gap region, in conjunction with theaccompanying disc friction.

Various attempts to deal with this problem have already been undertaken.In this respect, reference may be made merely to a proposal which waspublished under the definition “Polar Sealing” by VA TECH VOEST MCEdescribed in (EP 1 098 088) and in which, in the outer region of therotor, from the casing outwards, an ice bead is formed by cooling,which, during operation, grows as far as the rotor and comes to bearthere in a slightly abrading manner and thus assumes sealing. This is anoutstanding example of how difficult it is to seal off in this region ofa Francis turbine when one of the leading international companies in thefield of the production of turbines of this type proposes such acomplicated self-regenerating seal.

The problems associated with this seal are, above all, the risk ofbreakage of at least part of the ice ring and the subsequent leak, whichis why the publication proposes to provide this seal in addition to thetraditional labyrinth seal. Although a reduction in leakage and in theproblems connected with this can be achieved by means of this strategy,this is nevertheless at the expense of high investment and the use of acomplex additional component which requires additional maintenance andcare.

A solution with hydrostatic mounting is known from DE 25 54 217 A1(corresponds to U.S. Pat. No. 4,118,040 from the Search Report): in thiscase, a sealing ring is held via essentially tangentially running armsand is mounted sealingly in an annular groove of the casing. Thissealing with respect to the casing may take place via elastomeric ringsor similar elements which are mounted in the groove and which come tobear over a large area on the outer surfaces of the ring, thus, in turn,markedly obstructing the moveability of the latter in the axialdirection and thus adversely impairing the change in the gap heightbetween the ring and the rotor. However, in view of the unavoidableaxial movement of the rotor with respect to the casing, this change isabsolutely necessary in order to achieve as efficient a hydrostatic sealas possible. In a number of exemplary embodiments, the water requiredfor hydrostatic sealing is supplied via tubes or the like, thus furtherobstructing its moveability.

Another solution is known from CH 659 856 A5: a ring which isessentially immovable with respect to the casing is sealed off withrespect to the rotor (hub disc, cover disc) radially and in anon-contact manner by means of hydrostatic sealing, whilst, to improvethe rapid adjustability of the gap height, the ring is mounted with aslittle friction as possible in the axial direction likewise by means ofa type of hydrostatic mounting. The bearing water for the axial bearingis in this case branched off from the bearing water for the radialbearing. However, this ring is unavoidably also held on (a plurality of)radially running cylindrical supply lines for the bearing water and issealed off with respect to these lines by means of O-rings. Thismounting of the ring therefore cannot be designated as “floating”, sincethe change in the gap height in the radial bearing is markedlyobstructed by these O-rings. The entire construction of the seal iscomplicated and makes it necessary to adhere to a whole series of narrowtolerances on various components which have considerably largedimensions.

DE 196 11 677 A1 proposes a seal, designated as “non-contact”, with aring, designated as “floating”. The ring is in this case mounted on thecasing sealingly and in a rotationally fixed and elastically supportedmanner (and not non-contact), and the cylindrical surface directedtowards the rotor has two zones: one which performs the function of alabyrinth seal and one which performs a centring function. The leakageis thus used for centring the ring. There is therefore no hydrostaticbearing in the strict sense. In this proposal, there are major problemsin the mounting of the ring on the casing, since, of course, a goodmoveability of the ring and a leak-tight connection must be achievedsimultaneously. How this is to be solved satisfactorily is not stated.Other problems arise from the fact that, in the case of the low leakageto be sought after, centring can scarcely be achieved.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a seal which, in all thehydraulic turbomachines mentioned in the introduction, brings about amarkedly improved sealing action, as compared with the prior art, in asimple and reliable way.

According to the invention, to achieve these aims, there is provisionfor arranging in the peripheral region of the rotor an overhung sealingring which is mounted in a non-contact manner both with respect to therotor and with respect to the casing by hydrostatic floatation. By thedesignation “overhung” is meant, in this description and in the claims,that the bearing movements of the ring are not counteracted by any guideforces which in their magnitude would exceed the magnitude of the forcesof the hydrostatic mounting. In the prior art, forces of this type are,for example, the frictional forces of the elastomeric elements or thefrictional forces of the O-rings. By virtue of the invention, thequantity of gap water is drastically decreased, the disc friction isreduced by orders of magnitude and the axial thrust is appreciablydiminished. Since, according to the invention, the leakage consists onlyof bearing water, the risk of the penetration of foreign bodies into thesealing region and consequently the risk of damage to the seal aregreatly reduced.

In one embodiment of the invention, the ring is pressed by thesurrounding pressure of the water onto the rotor in the axial directionand onto the casing in the radial direction. Consequently, the mainmovement of the ring takes place in the axial direction, so as to followthe tilting and main deformation of the rotor in its outer region. Thisis advantageous because of the travel available in this direction.

Hydrostatic bearings in machine building and, in particular, inhydrodynamic machine building are known per se, but it has not beenpossible hitherto to use them between components, of which the distancefrom and position in relation to one another may change to an extentsuch as is the case, for example, on the outer circumference of a rotorof a Francis turbine. Only by the hydrostatic mounting according to theinvention with respect to both components is impossible to compensatethese tolerances and movements, without having to diminish the sealingaction and without having to fear collisions.

In one embodiment of the invention, there is provision for providing, inat least one of the two sealing surfaces between the sealing ring andthe rotor, hydrodynamic lubricating pockets, by way of which, inaddition to the hydrostatic mounting, a hydrodynamic bearing effectoccurs as a result of the relative movement between the sealing ring andthe rotor. The stability range of the seal, according to the invention,is thus further increased by way of the hydrodynamic bearing effect.

In a particularly preferred variant of the invention, there is provisionfor the water under pressure, required for the hydrostatic mounting ofthe sealing ring with respect to the rotor, to be supplied from ahydrostatic bearing between the casing and the sealing ring by way ofbores in the sealing ring. These bores extend to, at one end, thehydrostatic bearing relative to the casing and, at the other end, thehydrostatic bearing relative to the rotor.

Thus, any securing of the sealing ring against rotation becomessuperfluous, and there is no need for any water under pressure to besupplied to the sealing ring by way of flexible lines or the like.Furthermore, the bearing friction is substantially decreased as a resultof the sealing ring which rotates at approximately half the turbinerotational speed.

In one embodiment of this version, a hydrostatic bearing with twogrooves is provided between the casing and the ring. One groove isconnected by way of bores to at least one groove of the hydrostaticbearing of the ring with respect to the rotor. This makes it possible toprovide two separate feeds for the two bearings, with the result thatthe axial bearing can be uncoupled from the radial bearing in terms ofpressure and fluctuations in one bearing can thus be kept away from theother bearing. This makes an appreciable contribution to the stabilityof the mounting, more precisely to the bearing movement of the ring.

The invention also provides for a system for providing sealing between arotor and a turbine casing in a hydraulic turbomachine, wherein thesystem comprises a sealing ring arranged in a peripheral region of therotor. The sealing ring forms at least one hydrostatic bearing withrespect to at least one of the rotor and the turbine casing. The atleast one hydrostatic bearing comprises at least two bearing surfaceswhich face one another. At least one of the at least two bearingsurfaces is arranged on the sealing ring. At least another of the atleast two bearing surfaces is arranged on at least one of the rotor andthe turbine casing. At least one groove is formed on at least one of theat least two bearing surfaces. At least one pressure-liquid line iscoupled to each of the at least one groove and a pressure-liquid supply.

The pressure-liquid line may deliver water and the sealing ring maycomprise an overhung sealing ring. The one of the at least two bearingsurfaces of the sealing ring may comprise a radially outer cylindricalwall. The other of the at least two bearing surfaces may be arranged onthe turbine casing and comprises a radially outer cylindrical wall. Theturbine casing may comprise a turbine cover that includes an annularstrip, and the radially outer cylindrical wall of the turbine casing maybe arranged on the annular strip of the turbine cover. The sealing ringmay be non-rotatably mounted. The sealing ring may be secured againstrotation with respect to the turbine casing. The at least onepressure-liquid line may comprise a flexible line. The sealing ring maybe both flexibly suspended with respect to the turbine casing andsecured against rotation with respect to the turbine casing.

The sealing ring may be capable of moving at least one of axially withrespect to an axis of rotation of the rotor and essentially in a planeperpendicular to the axis. The sealing ring may be adapted to moveaxially with respect to an axis of rotation of the rotor. The sealingring may be adapted to move essentially in a plane perpendicular to anaxis of rotation of the rotor. The sealing ring may be adapted to moveeach of axially with respect to an axis of rotation of the rotor andessentially in a plane perpendicular to the axis.

The at least one pressure-liquid line may deliver liquid to the at leastone hydrostatic bearing. The sealing ring may comprise bores fordelivering liquid to at least one of the at least two bearing surfaces.The sealing ring may comprise bores for delivering liquid to each of theat least two bearing surfaces. The sealing ring and the turbine casingmay each comprise bores for delivering liquid. The bores of the sealingring and the turbine casing may be arranged to allow liquid to pass fromthe turbine casing to the sealing ring and from the sealing ring to therotor. The sealing ring may comprise first bores for delivering liquidand the turbine casing may comprise second bores for delivering liquid.The first bores may be arranged to allow liquid to pass from the turbinecasing to the sealing ring and the second bores may be arranged to allowliquid to pass from the sealing ring to the rotor.

The at least one pressure-liquid line may comprise a first pressure lineand a second pressure line, wherein the first pressure line is coupledto the first bores, and wherein the second pressure line is coupled tothe second bores. The at least one groove may comprise at least twogrooves spaced from one another. The first pressure line may deliverliquid to one of the at least two grooves and the second pressure linemay deliver liquid to another of the at least two grooves. The at leastone groove may comprise at least two grooves spaced from one another.

The at least two grooves may be arranged on an annular axial surface.The at least two grooves may be arranged on an annular axial surface ofthe sealing ring. The at least two grooves may be arranged on an outercircumferential surface. The at least two grooves may be arranged on anouter circumferential surface of the turbine casing. The at least twogrooves may be arranged on an inner circumferential surface. The atleast two grooves may be arranged on an inner circumferential surface ofthe sealing ring.

The invention also provides for a system for providing sealing between arotor and a turbine casing in a hydraulic turbomachine, wherein thesystem comprises a sealing ring arranged in a peripheral region of therotor. The sealing ring forms at least one hydrostatic bearing withrespect to at least one of the rotor and the turbine casing. The atleast one hydrostatic bearing comprises at least two bearing surfaceswhich face one another. At least one of the at least two bearingsurfaces is arranged on the sealing ring. At least another of the atleast two bearing surfaces is arranged on at least one of the rotor andthe turbine casing. At least one groove is formed on at least one of theat least two bearing surfaces. At least one pressure-liquid line iscoupled to each of the at least one groove and a pressure-liquid supply.The sealing ring rotates with respect to the turbine casing.

The sealing ring may rotate at a lower speed than the rotor. Theinvention also provides for a method of retrofitting a turbine using thesystem described herein, wherein the method comprises mounting thesealing ring to the turbine and sealing the rotor to the turbine casingwith the sealing ring.

The invention also provides for a system for providing sealing between arotor and a turbine casing in a hydraulic turbomachine, wherein thesystem comprises a sealing ring arranged in a peripheral region of therotor. The sealing ring comprises bores and forming a first hydrostaticbearing with respect to the rotor and a second hydrostatic bearing withrespect the turbine casing. At least one of the first and secondhydrostatic bearings comprises two bearing surfaces which face oneanother. At least one groove is formed on at least one of the twobearing surfaces. The at least one groove communicates with the bores ofthe sealing ring. At least one pressure-liquid line is coupled to eachof the at least one groove and a pressure-liquid supply. The sealingring is separated from each of the turbine casing and the rotor viagaps. The gaps may be in the range of between about 10 micrometers andabout 350 micrometers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to thedrawing in which:

FIG. 1 shows a Francis turbine according to the prior art;

FIG. 2 shows the region between the casing upper part and the rotorbottom of an embodiment according to the invention;

FIG. 3 shows a variant with a rotating sealing ring;

FIG. 4 a shows a particularly preferred embodiment of the variantaccording to FIG. 3;

FIG. 4 b shows a pressure profile chart representing the annular widthof the sealing region;

FIG. 4 c shows a pressure profile chart representing the annular lengthof the sealing region; and

FIG. 5 shows a variant of the sealing ring according to the invention,similar to that of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows diagrammatically a Francis turbine 1 according to the priorart, such as may be gathered from the book: “Rabe, HydraulischeMaschinen und Anlagen” (“Rabe, Hydraulic Machines and Plants”):

A rotor 3 rotates in a casing 2, the entry of the water taking place byway of a guide wheel 4 or its individual blades which are arrangedrotatably, but with a fixed axis 8, in the casing 2. The rotor 3 hasindividual ducts which run in a curved manner both in thecircumferential direction and with respect to the turbine axis 7, sothat the water leaves the rotor 3 downwards essentially in the axialdirection into the suction pipe 5.

Between the stationary casing 2 and the rotor 3, there are, of course,an upper gap or gap space 9 and a lower gap or gap space 10. The lowergap 10 leads to the loss of the gap water which passes into the regionof the suction pipe, without the energy contained in it being capable ofbeing worked off, but, apart from this loss, does not present anyfurther problems.

This is in contrast to the gap water which passes into the upper gapspace 9 between the rotor bottom 11 and the turbine cover 12. Since theturbine cover is closed off sealingly with respect to the rotating shaft6 by way of a gland-type seal 13, virtually the pressure of the upperwater (more precisely: the pressure before entry into the rotor) isestablished in this gap space 9. This leads to a considerable load onthe shaft 6 or on its axial bearing. Furthermore, as a result of thewater disc which is formed between the turbine cover 13 and the rotorbottom 11, considerable friction occurs, which, because of the highcircumferential speeds of the order of magnitude of 35 m/s and the largelever arm relative to the rotor axis 7 of nowadays usually a few meters,leads to pronounced torques which brake the shaft rotation.

In order to diminish these problems, the prior art provides, in theoutermost region of the rotor bottom 11, a labyrinth seal 14, thenarrowest gaps of which are in the region of an order of magnitude ofabout 1 mm. In order to avoid the pressure build-up, which may be up to30 bar and even above, leakage water is led through a relief line 15 viaa throttle 16 to the suction pipe 5. Furthermore, relief bores may alsobe provided.

According to the invention, it is proposed to provide between the casing2 and the turbine rotor 3, particularly, but not exclusively, at theperipheral region of the rotor bottom 11, a seal, by way of which theflow of the gap water is drastically reduced.

Such a seal according to the invention is illustrated diagrammaticallyin FIG. 2: the rotor 3 has provided on it a running track 17 which, inthe exemplary embodiment illustrated, is illustrated as a separateannular body. This does not have to be so, but the running track 17 mayalso be produced in one piece with the rotor 3 during the production ofthe latter, for example be lathe-turned or ground from the solid. Theactual sealing surface 18 runs perpendicularly to the axis of rotation 7of the turbine. One end face 20 of a sealing ring 19 co-operates with asealing surface 18. In the exemplary embodiment illustrated, thissealing ring is illustrated in its simplest form with rectangular crosssection. As explained in more detail further below, this form may bevariously modified and be adapted to the particular features of therespective application.

The sealing ring 19 is stationary with respect to the casing cover 12,which means that it does not co-rotate with the rotor bottom 11.However, the sealing ring 19 is axially displaceable, within particularlimits, with respect to the casing, in particular with respect to theturbine cover 12, as is explained in more detail below. A plurality ofbut at least one, flexible pressure-water lines 21 lead out of theregion of the turbine cover 12 to the sealing ring 19. The sealing ring19 has, if appropriate, inside it, at least one annular duct which opensinto an annular groove on its lower end face 20 or merges into thisgroove or is formed by it. Pressure water supplied by way of thepressure-water lines 21 forms, in co-operation with the groove and withthe sealing surface 18 located opposite it, a hydrostatic bearing forthe sealing ring 19. The bearing gap in this case has a gap height inthe range of about 10 micrometers to 350 micrometers, preferably about100 to 250 micrometers, and is therefore narrow, as compared with thegap widths of the conventional labyrinth seal (FIG. 1).

It has not been possible to employ such a hydrostatic seal known per sein the present field of use on account of the extreme relative speeds,as already mentioned further above, in the region of an order ofmagnitude of 35 m/s and, above all, in view of the high pressures (30bar and above) which occur and of the axial movements of the rotor 3with respect to the turbine cover 12 which are considered too great forthe use of hydrostatically mounted sealing rings, to be precise becauseit is necessary to guide the sealing ring 19 in the axial direction andthis guidance has always failed hitherto as a result of the operatingconditions outlined.

According to the invention, the problems associated with this aresolved, in that the sealing ring 19 is guided on the turbine cover 12moveably in the axial direction by way of a cylindrical hydrostaticbearing. This bearing is constructed as follows:

The turbine cover 12 has an annular strip 23 which projects in the axialdirection towards the rotor 3 and of which the outer cylindrical surface(if appropriate, with a coating similar to that of the sealing surface18) serves as a bearing surface 24. For this purpose, at least onegroove 25 is provided in this bearing surface 24, and, as is customaryin hydrostatic bearings, pressure water is supplied to the groove by wayof at least one pressure-water line 22. Between the sealing ring 19 andthe turbine cover 12, a mounting is thereby provided, which allows thesealing ring to execute a virtually friction-free movement in the axialdirection. In addition, by virtue of this mounting, a “tilting” of thesealing ring 19 (actually, torsion or rolling-up) is reliably avoided.Such tilting of the sealing ring 19 is perfectly possible, without suchguidance or mounting, under the dynamic loads acting on it and leads tothe collapse of the sealing co-operation between the sealing ring 19 andthe sealing surface 18.

The inventive solution to the sealing problem is beneficial not onlydynamically, but also in energy terms and entails relatively simple andlow investments. The pressure water for the two hydrostatic bearingsurfaces can be extracted from the upper water of the turbine, so that(because of the centrifugal acceleration in the region of the sealinggap) no or only low pump capacity is necessary for overcoming theremaining pressure difference. Part of the pressure water flows radiallyoutwards and thus passes into the rotor, so that a corresponding part ofthe invested pump capacity is recovered in the turbine. It is alsoessential that the penetration of foreign bodies is reliably avoided dueto the radially outflowing pressure water. The components to be arrangedon the rotor 3 and in the turbine casing 2 require scarcely any space,but in any case all events, less space than the previous labyrinth seal,and it is therefore also possible to retrofit existing turbinescorrespondingly.

Since the operating temperature of turbines is determined by thetemperature of the water used, there are no problems of thermalexpansion, even at the cylindrical gap between the sealing ring 19 andannular strip 23, in spite of the narrow gap height which is to besought after.

FIG. 3 shows a detail of the particularly preferred embodiment with arotating sealing ring 19′. Here pressure water is supplied to thecylindrical wall surface of the annular strip 23 by way of thepressure-water line 22′ and builds up the hydrostatic bearing alreadydescribed between the annular strip 23 and the sealing ring 19′ which inthis case has a groove 25′. Part of the water supplied to the groove 25′in this way passes through bores 26′ into the region of the groove 27 onthe axial end face 20 of the sealing ring 19′ and there, as justdescribed above, builds up the hydrostatic bearing between the rotor 3and the sealing ring 19′.

The flexible pressure-water lines 21 and the securing against rotationconsequently become obsolete, without disadvantages having to beaccepted. Quite to the contrary, the frictional losses are appreciablyreduced by way of the sealing ring 19′ rotating at approximately halfthe turbine rotational speed. Owing to the simple construction, thisvariant is also particularly suitable for subsequent installation inexisting Francis turbines.

The number, dimensions and configurations of the bores 26′ can easily bedetermined by a person skilled in the field of hydrodynamics, with aknowledge of the invention and of the respective requirements, and canbe adapted to various operating conditions. Thus, it is possible to haveoblique bores which are continuously straight from groove to groove(more precisely: from bearing surface to bearing surface, since, ofcourse, the grooves may also be arranged in the opposite bearingsurface).

The invention can be embodied in many ways and be adapted to existing orgiven conditions. Thus, it is not necessary for the sealing ring 19, 19′to have the rectangular form illustrated. It is perfectly possible toprovide it with an L-shaped or other cross section and thus ensure thebest possible adaptation of the sealing ring to the geometric anddynamic conditions. The surface of the sealing ring may be provided, inthe region of the two bearings, with claddings, coverings or coatings,in order to avoid damage in the event of contact with the oppositesurfaces.

Of course, it is possible, in particular, to provide the bearing surfacebetween the sealing ring 19 and the rotor 3 with a plurality of grooveswhich, if appropriate, lie at least partially next to one another, andthis may be advantageous particularly when the hydrostatic bearing thusformed is not to be designed as a (circumferentially) continuousbearing, but consists of a plurality of portions corresponding, forexample, to sectors. The run of the (individual) groove (or grooves) isthen not necessarily in the form of an arc of a circle, but may bespiral. A subdivision may be advantageous, in order, in the event of thepenetration of foreign bodies or dirt, to ensure that the collapse ofthe hydrostatic mounting does not occur. It may happen that, if dirtenters, there is an insufficient supply of pressure water in individualgeometrically delimited parts of the sealing surface completely, butthis can be compensated by providing on the sealing ring 19 a pluralityof bearing portions which are independent of one another and which, ifappropriate, overlap one another correspondingly.

The pressure water supply to the two bearings flows essentially alongthe arrows (having fully inked tips) out of the actual bearing regionand thus contributes to ensuring that no foreign bodies pass into theregion of the narrow bearing gaps (FIG. 2).

The sealing ring 19 requires no axial pressing, the latter taking placeby way of the pressure (indicated by the arrows with dashed tips) of thegap water surrounding it (surrounding pressure p1), but, under somecircumstances, it is advantageously possible to provide a device forslight pressing (springs or the like), in order to hold the sealing ringin a predetermined position in the event of the standstill of theturbine after an operating intermission or an inspection has takenplace. An emergency lift-off may likewise be provided for the sealingring, for example in the event of an insufficient pressure of thepressure water.

FIG. 4 a shows a particularly preferred variant of the invention. Theessential difference from FIG. 3 is that a hydrostatic bearing with twogrooves 25″ and 28″ is provided in the sealing region between theannular strip 23″ and the sealing ring 19″. In this case, the groove 25″serves, in a similar way to the hydrostatic bearing groove 25 in FIG. 2,for non-contact mounting between the sealing ring 19″ and the annularstrip 23″, and the groove 28″ ensures, by way of bores 26″, the deliveryof pressure water to the hydrostatic bearing by way of the groove 27″between the sealing ring 19″ and the rotor 3. This makes it possible,even with the sealing ring 19″ rotating, to provide the two bearings27″, 28″ with pressure water separately from one another, when onlyseparate delivery lines 21″ and 22″ are provided.

In a further embodiment (FIG. 5), the sealing ring 19″ has provided init, instead of the groove 27′″, depicted in as being wide, two narrowergrooves 27″ which are at a distance from one another and which are eachfed independently from the groove 28″ by way of bores 26″. The stabilityof the mounting of the sealing ring 19″ on the rotor 3 is consequentlyfurther increased.

This separation of the pressure-water supply of the two bearings has theresult that, in the event of a change in the height of one of the twogaps, the pressure in the other gap (and consequently its height) isinfluenced to a substantially lesser extent than in the variantillustrated in FIG. 3, and, ideally, not at all. This not only improvesthe stability of the hydrostatic mounting in general, but, inparticular, may damp periodic movements of the sealing ring or preventthem from being excited.

In this connection, the pressure-water supply will be dealt withbriefly. It is advantageous and, under some circumstances, necessary toensure that, in the event of a rise in the throughput in one of the (orsome adjacent) supply lines, the throughflow remains as far as possibleunchanged in the adjacent or other supply lines. However, this caneasily be determined by a person skilled in the field of fluidmechanics, with a knowledge of the invention and of the boundaryconditions, by way of corresponding dimensioning or co-ordination of thecross sections and/or the provision of corresponding throttles in theindividual supply lines. A factor in achieving this aim is that thecross section of the bores provided in the sealing ring for supplyingthe axial seal is such (in the examples illustrated) that thethroughflow of the pressure water takes place as far as possible free ofloss.

In FIGS. 4 a and 4 b, the pressure profile is illustrated, respectively,against the seal width and length between the sealing ring 19″ and thecasing or the sealing ring 19″ and the rotor 3: in this case, p1 standsfor the pressure prevailing upstream of the sealing ring and p2 for thepressure downstream of the sealing ring in the gap between the annularstrip 23″ and the rotor bottom 11, as also explained above withreference to FIG. 1. As is clear, the pressure profiles can beinfluenced to a great extent by the position and dimensioning of thegrooves 25″, 28″ and 27″ and the position of these profiles in relationto the pressure p1 can be influenced to a great extent by the selectionof the pressures prevailing in the supply lines 21″ and 22″. For aperson skilled in the field of fluid mechanics, with a knowledge of theinvention, this is not difficult and makes it possible to adapt to themost diverse boundary conditions.

Finally, it is possible to provide, in the region of the bearing surfaceor bearing surfaces between the sealing ring 19, 19′, 19″ and thecomponents rotating opposite it, hydrodynamic lubricating pockets on atleast one of the two bearing surfaces located opposite one another, inorder to provide hydrodynamic mounting in addition to the hydrostaticmounting.

FIG. 5 shows a variant of a sealing ring, in which the supply of theaxial seal takes place by way of bores 26″ which emanate from the“lower” region (groove 28″) of the radial seal. Here, furthermore, theaxial bearing is different from that illustrated in FIG. 4, in that ithas two grooves 27′″ which are each supplied independently with pressurewater. This change has no influence on the functioning of the bearing,since, of course, the hydrostatic pressure also builds up in the sameway between the grooves. The sealing ring 19″ of FIG. 5 has anessentially rectangular, but not square cross section, the annular widthRB≠the annular height RH, and an asymmetric shoulder 29 is formed at thelocation of the gap between the casing and the rotor. It is therebypossible to compensate “rolling-up moments” acting on the sealing ring(equilibrium of moments) and to reduce the deformations of the sealingring which are induced by them. In view of the bearing gaps which areonly about 10 micrometers to 350 micrometers high, deformations of thiskind are to be avoided as far as possible.

In the drawings, the seal between the sealing ring 19, 19′, 19″ and thecasing 2 is always illustrated as a radial seal and the seal between thesealing ring and the rotor 11 as an axial seal. This may, of course,also be reversed and, for the run of the casing-side supply lines, mayalso afford advantages when, even if, in an arrangement of this typewith a rotating sealing ring, the pressure water has to be conveyedcounter to centrifugal acceleration in the sealing ring.

The sealing ring 19, 19′, 19″ and those surfaces of the rotor bottom 11and of the turbine cover 2 which co-operate with it may consist of thematerials conventionally used in hydrostatic seals, thus the surface 24of the annular strip 23 (or this itself) or the surface of the runningtrack 17 may consist of steel or of a bearing metal, and the sealingring 19 may be formed from steel or likewise from a bearing metal orelse from aluminium or an aluminium alloy. Of course, it is alsopossible, and in many cases advisable, to manufacture at least thesealing ring 19, 19′ from a plastic, in particular a fibre-reinforcedplastic, or from a ceramic material.

It is also conceivable, in an embodiment similar to that of FIG. 2, toprovide both grooves of the hydrostatic bearing in the sealing ring 19and to dispense with the pressure-water line 22, virtually to provide acounterpart to the variant of the co-rotating sealing ring 19′. Thesealing ring 19 may be secured against co-rotation with the rotor bottom11 in various ways, either by way of a shoulder and countershoulder orelse by way of a correspondingly flexible and symmetrical suspension ofthe sealing ring on the turbine cover 12, the suspension preferablylying in a plane perpendicular to the turbine axis 7, so as not totransmit any appreciable forces in the axial direction and so as not todisturb the axial movement of the sealing ring with respect to theannular strip 23 by friction.

The invention has been discussed with reference to examples which relateto the most important seal in the area of Francis turbines, but it isclear to a person skilled in the art that the invention can also beapplied advantageously at the other sealing points of Francis turbinesand, of course, in all other hydraulic turbomachines, whether pumps orturbines, in all the gaps between their casing and their rotor.

The entire description and the claims speak of “pressure water” or“bearing water”, but, of course, in special fields of use (for example,pumps in food technology), another liquid may be used instead of water,without departing from the of the invention. Finally, fields of use, inparticular apart from Francis turbines, may be envisaged, in which thehydrostatic bearings are designed without grooves.

1. An arrangement for sealing-off a rotor of a hydraulic turbomachinewith respect to a turbine casing, wherein, in a peripheral region of therotor, an overhung sealing ring is arranged and is mounted both withrespect to the rotor and with respect to the turbine casing, in eachcase the arrangement includes at least one hydrostatic bearing, whereineach of the hydrostatic bearings has bearing surfaces facing oneanother, wherein at least one groove extends into at least one of thebearing surfaces, and wherein at least one pressure-water line, which isconnected to a pressure-water supply, supplies pressure liquid into atleast one of the bearing surfaces and the overhung sealing ring issecured against rotation with respect to the turbine casing.
 2. Thearrangement of claim 1, wherein the turbine casing comprises a radiallyouter cylindrical wall and an annular strip.
 3. The arrangement of claim1, wherein the at least one pressure-water line is a flexiblepressure-water line.
 4. The arrangement of claim 1, wherein a flexiblepressure-water line is coupled to each of the turbine casing and theoverhung sealing ring.
 5. The arrangement of claim 1, wherein the atleast one pressure-water line supplies pressure liquid to the bearingsurface between the turbine casing and the overhung sealing ring, andwherein the overhung sealing ring has bores which supplies the pressureliquid to the bearing surface of the overhung sealing ring which formsone of the hydrostatic bearings with the bearing surface of the rotor.6. The arrangement of claim 1, wherein the at least one pressure-waterline comprises two pressure-water lines arranged at an axial distancefrom one another, the two pressure-water lines being disposed in theturbine casing and supplying pressure liquid to the bearing surfacebetween the turbine casing and the overhung sealing ring, wherein one ofthe two pressure-water lines is located opposite a bore of the overhungsealing ring, and wherein the bore supplies pressure liquid to thebearing surface of the overhung sealing ring opposite the bearingsurface of the rotor.
 7. The arrangement of claim 1, wherein the atleast one pressure-water line comprises a first pressure-water linesupplying pressure liquid to the hydrostatic bearing between theoverhung sealing ring and the rotor and a second pressure-water linesupplying pressure liquid to the hydrostatic bearing between theoverhung sealing ring and the turbine casing and wherein the first andsecond pressure-water lines supply pressure liquid independently of oneanother.
 8. A system for providing sealing between a rotor and a turbinecasing in a hydraulic turbomachine, the system comprising: an overhungsealing ring for providing sealing between the rotor and the turbinecasing; the sealing ring being arranged in a peripheral region of therotor and comprising at least two bearing surfaces; a first hydrostaticbearing being formed by at least one of the at least two bearingsurfaces and a surface of the turbine casing; and a second hydrostaticbearing being formed by at least another of the at least two bearingsurfaces and a surface of the rotor, wherein pressure-liquid isdelivered to each of the first and second hydrostatic bearings, whereinthe sealing ring follows movement of an outer region of the rotor, andwherein the sealing ring rotates with respect to the turbine casing. 9.The system of claim 8, further comprising at least one groove arrangedon at least one of the bearing surfaces.
 10. The system of claim 8,further comprising at least one pressure-liquid line coupled to at leastone of the at least two bearing surfaces and a pressure-liquid supply.11. The system of claim 8, further comprising at least onepressure-liquid line coupled to a pressure-liquid supply and to at leastone groove arranged on at least one of the bearing surfaces.
 12. Thesystem of claim 8, wherein the turbine casing comprises a radially outercylindrical wall.
 13. The system of claim 8, wherein the surface of therotor is arranged on an annular wall.
 14. The system of claim 13,wherein the turbine casing comprises a turbine cover that includes anannular strip, and wherein a radially outer cylindrical wall of theturbine casing is arranged on the annular strip of the turbine cover.15. The system of claim 8, further comprising at least one flexiblepressure-liquid line supplying pressure-liquid to one of the first andsecond hydrostatic bearings.
 16. The system of claim 8, wherein thesealing ring is flexibly suspended with respect to the turbine casing.17. The system of claim 16, wherein the sealing ring can move axiallywith respect to an axis of rotation of the rotor and essentially in aplane perpendicular to the axis.
 18. The system of claim 8, wherein thehydraulic turbomachine comprises a Francis turbine.
 19. The system ofclaim 8, wherein the sealing ring comprises a rectangular cross-section.20. The system of claim 19, wherein the at least two bearing surfaces ofthe sealing ring comprise only two bearing surfaces, one of the twobearing surfaces being an inner peripheral surface of the sealing ringand another of the two bearing surfaces being an annular surface of thesealing ring.
 21. The system of claim 8, further comprising at least onepressure-liquid line which delivers liquid to the first and secondhydrostatic bearings.
 22. The system of claim 8, wherein the sealingring comprises bores for delivering liquid to at least one of the firstand second hydrostatic bearings.
 23. The system of claim 8, wherein thesealing ring comprises bores for delivering liquid to each of the firstand second hydrostatic bearings.
 24. The system of claim 8, wherein eachof the sealing ring and the turbine casing comprises bores fordelivering liquid.
 25. The system of claim 24, wherein the bores of thesealing ring and the turbine casing are arranged to allow liquid to passfrom the turbine casing to the sealing ring and from the sealing ring tothe rotor.
 26. The system of claim 8, wherein the sealing ring comprisesfirst bores for delivering liquid and wherein the turbine casingcomprises second bores for delivering liquid.
 27. The system of claim26, wherein the second bores are arranged to allow liquid to pass fromthe turbine casing to the sealing ring and wherein the first bores arearranged to allow liquid to pass from the sealing ring to the rotor. 28.The system of claim 27, further comprising a first pressure line and asecond pressure line, wherein the first pressure line is coupled to eachof the first and second bores, and wherein the second pressure line iscoupled to the second bores.
 29. The system of claim 28, wherein thesealing ring comprises at least two grooves spaced from one another. 30.The system of claim 29, wherein the first pressure line delivers liquidto one of the at least two grooves and wherein the second pressure linedelivers liquid to another of the at least two grooves.
 31. The systemof claim 8, wherein the sealing ring comprises at least two groovesspaced from one another.
 32. The system of claim 31, wherein the atleast two grooves are arranged on an annular surface which faces anannular surface of the turbine casing.
 33. The system of claim 31,wherein the at least two grooves are arranged on only one annularsurface of the sealing ring.
 34. The system of claim 31, wherein the atleast two grooves are arranged on an outer circumferential surface. 35.The system of claim 31, wherein the turbine casing comprises an outercircumferential surface.
 36. The system of claim 31, wherein the atleast two grooves are arranged on an inner circumferential surface. 37.The system of claim 8, wherein the surface of the rotor is arranged on arunning track which projects out from the peripheral region of therotor, the running track being one of a separate annular body and formedwith the rotor as one piece.
 38. A method of retrofitting a turbineusing the system of claim 8, the method comprising: mounting the sealingring to the turbine; and sealing the rotor to the turbine casing withthe sealing ring.
 39. A system for providing sealing between a rotor anda turbine casing in a hydraulic turbomachine, the system comprising: asealing ring arranged in a peripheral region of the rotor; the sealingring forming at least one hydrostatic bearing with respect to the rotorand at least another hydrostatic bearing with respect to the turbinecasing; each hydrostatic bearing being formed by at least two bearingsurfaces which face one another; at least one groove being arranged onat least one of the hydrostatic bearings; and at least onepressure-liquid line coupled to each of the at least one groove and apressure-liquid supply, wherein the sealing ring rotates with respect tothe turbine casing.
 40. The system of claim 39, wherein the sealing ringrotates at a lower speed than the rotor.
 41. A system for providingsealing between a rotor and a turbine casing in a hydraulicturbomachine, the system comprising: an overhung sealing ring arrangedin a peripheral region of the rotor; the sealing ring comprising boresand forming only one hydrostatic bearing with respect to the rotor andonly one hydrostatic bearing with respect to the turbine casing; atleast one of the first and second hydrostatic bearings comprising twobearing surfaces which face one another; at least one groove beingformed on at least one of the two bearing surfaces; the at least onegroove communicating with the bores of the sealing ring; and at leastone pressure-liquid line coupled to each of the at least one groove anda pressure-liquid supply, wherein the sealing ring is separated fromeach of the turbine casing and the rotor via gaps and the sealing ringrotates with respect to the turbine casing.
 42. The system of claim 41,wherein the gaps are in the range of between about 10 micrometers andabout 350 micrometers.
 43. A system for providing sealing between arotor and a turbine casing in a hydraulic turbomachine, the systemcomprising: an overhung sealing ring arranged in a peripheral region ofthe rotor; the sealing ring forming at least one hydrostatic bearingwith respect to the rotor and at least another hydrostatic bearing withrespect to the turbine casing; each hydrostatic bearing being formed byat least two bearing surfaces which face one another; at least onegroove being arranged on at least one of the bearing surfaces; and atleast one pressure-liquid line coupled to a pressure-liquid supply andat least one of: at least one of the bearing surfaces and the at leastone groove, and wherein the sealing ring rotates with respect to theturbine casing.
 44. The system of claim 43, wherein one of the bearingsurfaces is arranged on a radially outer cylindrical wall of the turbinecasing.
 45. The system of claim 43, wherein one of the bearing surfacesis arranged on an annular wall of the rotor.
 46. The system of claim 43,wherein the sealing ring is secured against rotation with respect to theturbine casing.
 47. The system of claim 43, wherein the at least onepressure-liquid line comprises a flexible line.
 48. The system of claim43, wherein the sealing ring is flexibly suspended with respect to theturbine.
 49. The system of claim 48, wherein the sealing ring can moveboth mainly axially with respect to an axis of rotation of the rotor andessentially in a plane perpendicular to the axis.
 50. The system ofclaim 48, wherein the sealing ring can move axially with respect to anaxis of rotation of the rotor.
 51. The system of claim 48, wherein thehydraulic turbomachine is a Francis turbine.
 52. The system of claim 48,wherein the sealing ring can move each of axially with respect to anaxis of rotation of the rotor and essentially in a plane perpendicularto the axis.
 53. The system of claim 43, wherein the at least onepressure-liquid line delivers liquid to each of the hydrostaticbearings.
 54. The system of claim 43, wherein the sealing ring comprisesbores for delivering liquid to at least one of the bearing surfaces. 55.The system of claim 43, wherein the sealing ring comprises bores fordelivering liquid to each of the bearing surfaces.
 56. The system ofclaim 43, wherein each of the sealing ring and the turbine casingcomprises bores for delivering liquid.
 57. The system of claim 56,wherein the bores of the sealing ring and the turbine casing arearranged to allow liquid to pass from the turbine casing to the sealingring and from the sealing ring to the rotor.
 58. The system of claim 43,wherein the sealing ring comprises first bores for delivering liquid andwherein the turbine casing comprises second bores far delivering liquid.59. The system of claim 58, wherein the second bores are arranged toallow liquid to pass from the turbine casing to the sealing ring andwherein the first bores are arranged to allow liquid to pass from thesealing ring to the rotor.
 60. The system of claim 59, wherein the atleast one pressure-liquid line comprises a first pressure line and asecond pressure line, wherein the first pressure line is coupled to eachof the first and second bores, and wherein the second pressure line iscoupled to the second bores.
 61. The system of claim 43, wherein thesealing ring forms only one hydrostatic bearing with respect to therotor and only one hydrostatic bearing with respect to the turbinecasing.
 62. The system of claim 43, wherein the at least one groovecomprises at least two grooves spaced from one another.
 63. The systemof claim 62, wherein the at least two grooves are arranged on an annularsurface.
 64. The system of claim 62, wherein the at least two groovesare arranged on an annular axial surface of the sealing ring.
 65. Thesystem of claim 62, wherein the at least two grooves are arranged on anouter circumferential surface.
 66. The system of claim 62, wherein theat least two grooves are arranged on an outer circumferential surface ofthe turbine casing.
 67. The system of claim 62, wherein the at least twogrooves are arranged on an inner circumferential surface.
 68. The systemof claim 62, wherein the at least two grooves are arranged on an innercircumferential surface of the sealing ring.
 69. The system of claim 43,wherein the sealing ring rotates at a lower speed than the rotor.
 70. Amethod of retrofitting a turbine using the system of claim 43, themethod comprising: mounting the sealing ring to the turbine; and sealingthe rotor to the turbine casing with the sealing ring.